Mercury alert: Is canned tuna safe to eat?

The humble tuna fish sandwich is a lunchbox staple, and the second most popular seafood in the U.S. It's an affordable and versatile source of lean protein and some varieties are even high in heart-healthy omega-3s. But several species of tuna, like other large ocean fish, contain higher-than-average amounts of mercury.

This is of particular concern for young children, whose nervous system, brain, heart, kidneys and lungs are all susceptible to the harmful effects of mercury.

But parents and kids need not give up their tuna sandwiches altogether. The information below can help you minimize mercury intake while keeping healthy fish options in your child's diet.

How much canned tuna is safe to eat?

There are two main kinds of canned tuna: chunk light and solid or chunk white (albacore). Albacore is a larger species of tuna, with mercury levels almost three times higher than those of the smaller skipjack, which is used in most canned light tuna.

For this reason, parents should be especially mindful of their kids' tuna consumption. The recommendations below are based on EPA's guidance and current estimates of average mercury content in the two most popular types of canned tuna:

• Canned white, or albacore (0.32 parts per million of mercury). Children up to age six can eat up to one 3-ounce portion a month; children ages 6–12, two 4.5-ounce portions a month. Adults, including pregnant women, can safely eat it up to three times a month (women, 6-ounce portions; men, 8-ounce portions). Luckily, some brands of canned or pouch albacore contain significantly less mercury than well-known national brands, since they use smaller, lower-mercury fish (see box).

• Canned light — the safer choice (0.12 parts per million of mercury). Children up to age six can eat it up to three 3-ounce portions per month. Older children and adults can safely eat it once a week. But products labeled “gourmet” or “tonno” may contain mercury levels comparable to canned white, since they are made with bigger yellowfin tuna. Therefore, watch out for this label and eat it less often.

• A better alternative is canned salmon (mostly sockeye or pink from Alaska), which is low in contaminants and high in heart-healthy omega-3s. It's also sustainably caught in Alaska and similarly priced, making it a great choice all around.

Parents: Keep an eye on school lunches 

A new study by the Mercury Policy Project found a wide range of mercury levels in both light and white tuna from government sponsored school lunch programs. Some of the canned albacore/white tuna tested had mercury levels almost four times the average level reported by FDA. For unknowing school children, this means exposure to potentially dangerous mercury levels.

The bottom line is if your child eats tuna at school, it's best to find out what types are being offered (and how often). To be on the safe side, it’s probably best to opt for light tuna or canned salmon, especially if your child eats a lot of fish.

Marika Cowen

FDA’s guidance is lacking

The research mentioned above also calls on the Food and Drug Administration (FDA) to revise its woefully out-of-date mercury standards for fish, and we agree.

That’s one reason EDF originally developed its Seafood Selector health advisories in the first place, so that consumers could choose sustainable and healthy seafood with confidence. And more recently, Oceans expert Timothy Fitzgerald published a study in partnership with Stony Brook University that establishes the most comprehensive database on mercury levels in seafood to date.

How does mercury get into tuna?

Mercury is emitted from coal-fired power plants and other industrial sources. It drifts through the atmosphere and rains down on rivers, lakes and the ocean.

Once in the water, bacteria convert the metal into toxic methylmercury, which builds up in the tissues of marine animals. As bigger fish eat smaller fish, mercury accumulates, so top predators like tuna, king mackerel and swordfish are the most contaminated.

Stopping mercury pollution is essential to keeping fish safe to eat.